1. Field of the Invention
The present invention relates to a light source device configured to combine light from a plurality of solid-state light sources so as to excite a phosphor, and a projection display apparatus illuminating an image on a light valve with illumination light from the light source device so as to magnify and project the image.
2. Description of Related Art
A discharge lamp has been used widely as a light source of a projection display apparatus that uses a light valve composed of a liquid crystal or a mirror-deflection type digital micromirror device (DMD). However, since the discharge lamp has the problem of a short life, the reliability is low. Therefore, in order to solve this problem, recently, solid-state light sources such as a semiconductor laser and a light-emitting diode have been studied for use as the light source of the projection display apparatus.
FIG. 10 shows a configuration disclosed in JP 2004-341105 A as an example of a conventional projection display apparatus using a solid-state light source and a DMD. Ultraviolet light from a light-emitting diode 101 enters a disk-shaped color wheel 102. On the color wheel 102, a reflective film for transmitting ultraviolet light and reflecting visible light is formed. The exit-side surface of the reflective film is divided in a circumferential direction of the disk into three regions, and red, green and blue phosphor layers are formed on the respective regions, so that red, green and blue color lights are emitted by the incident ultraviolet light. The emitted light is transmitted through and reflected by a relay lens 103, a reflection mirror 104 and a prism 105, thereby entering a DMD 106. The light entered is modulated by the DMD 106 in accordance with a video signal, and the modulated light is magnified and projected by a projection lens 107.
Generally, the solid-state light source such as a light-emitting diode and a semiconductor laser emits lower amounts of light beams as compared with the discharge lamp. Because of this, it is difficult for the configuration shown in FIG. 10 to obtain high brightness. Therefore, studies have been done to obtain high-brightness light beams by combining light from a plurality of solid-state light sources.
FIG. 11 shows an exemplary light source device disclosed in U.S. Pat. No. 6,240,116 A, which is configured for combining light beams from a plurality of solid-state light sources with high density. A solid-state light source unit is composed of a laser bar 112 including pluralities of semiconductor lasers 110 and heat-dissipation plates 111, and a cooling unit 113. Each of light beams 114 exiting from the solid-state light source unit is condensed by a corresponding lens 115 and reflected by a stepped reflective surface 117 of a reflector 116. A width A of exiting light beams from the reflector 116 is smaller than a width B of light beams from the laser bar 112. Thereby, it is possible to obtain light beams combined densely and configure a compact solid-state light source device.
In the case of the light source device combining a plurality of solid-state light sources, in view of cooling performance, the plurality of solid-state light sources are disposed discretely at a predetermined interval. Therefore, as the number of the solid-state light source increases, an outline of exiting light beams becomes larger, which increases the size of the light source device.
The configuration described in U.S. Pat. No. 6,240,116 A that uses the stepped reflective surface 117 shown in FIG. 11 is effective in view of downsizing the solid-state light source unit composed of a plurality of solid-state light sources (semiconductor lasers 110) of a relatively small number. In other words, the divergence angle of the light beams from the solid-state light sources substantially is ±10° in a narrow direction, and a focal length of the condensing lens 115 may be determined so that light of this angle is taken in and converted into parallel light.
However, when light from an increased number of solid-state light sources is condensed within a predetermined outline of exiting light beams, the periodic interval of the semiconductor lasers 110 becomes narrow. Because of this, when the condensing lens 115 of the same focal length is used, the angle for condensing light becomes small, and hence light from the semiconductor lasers 110 cannot be condensed efficiently. On the other hand, when the condensing lens 115 of shortened focal length is used so as to narrower the width of exiting light beam from a single solid-state light source, an influence due to displacement between an emitting point of the condensing lens 115 and an emitting point of the solid-state light source increases, which increases the light loss during a transmission along a long optical path.